Tetrachloroethylene, or PCE, is a commercially important chlorinated hydrocarbon solvent and chemical intermediate. Currently almost half a billion pounds are manufactured in this country annually, with even larger amounts imported. At present slightly more than half is used in drycleaning and textile processing, often in very small and geographically dispersed facilities nationwide. A further 10% is used as a metal cleaning (degreasing) agent, again in small, often poorly controlled facilities such as garages and machine shops. Undoubtedly this pattern of use has contributed to the frequency with which PCE has shown up as a contaminant in drinking water supplies. In addition many more individuals are exposed by inhalation to high levels at work. Thus the carcinogenic potential of PCE is a matter of significant public health concern. Both epidemiological and toxicological data implicates PCE as a carcinogen. This project will test the hypothesis that PCE found in the distribution systems of public drinking water supplies in the Cape Cod region of Massachusetts is associated with any of five different types of cancer: lung, breast, colorectal, pancreas and brain. This will be accomplished by: 1. Estimating exposure to PCE in both cancer cases and controls using an already developed exposure model; 2. Analyzing the relationship between case-control status and estimated PCE exposure.